The research proposed here seeks to combine two diverse methodologies that have been used to study emotional phenomenon. There is a growing corpus of research from animal and human studies linking the startle to affective states. There is also a large body of research on children who show extreme levels of behavioral inhibition when presented novel stimuli, indicating that there are neurophysiological differences that set them apart from their uninhibited peers. The proposed studies investigate how neurophysiological indices of behavioral inhibition, such as heart rate variability, may also index differences in affective picture processing, as measured using the startle probe. The first study proposed examines responses in children who show differences in heart rate variability as a function of their classification as either inhibited of uninhibited. The second study using the startle probe methodology to investigate children's individual differences in affective picture processing. Pleasant, neutral, and unpleasant pictures will be shown to inhibited and uninhibited children and startle probes will be delivered during picture viewing. Startle responses will be used to determine affective processing in the children. The third study extends the work done in the second study to include anticipatory anxiety. Inhibited and uninhibited children will get startle probes while awaiting a warned aversive event. A noise blast will be given to participants 20 seconds after a warning tone. During that waiting period a startle probe will be delivered and the size of the participant's response will be used to determine affective state.